This invention relates to a method for preparing a N-substituted carboxamide polymer, particularly to a method for preparing a quaternized, N-substituted carboxamide polymer.
Quaternized, N-substituted carboxamide polymers are known to be effective thickeners and flocculating agents in aqueous solutions. Accordingly, the quaternary carboxamide polymers are useful in the clarification of aqueous systems, in paper making operations, in the treatment of sewage and industrial wastes, and as stabilizers for drilling muds and enhanced oil drilling operations.
Heretofore, quaternary carboxamide polymers have been prepared by a variety of methods. For example, in one prior art method, a carboxamide polymer is initially aminomethylated using formaldehyde and a secondary amine and, the aminomethylated polymer subsequently contacted with an alkylating agent such as dimethyl sulfate or methyl chloride. See, for example, British Pat. Nos. 1,373,034 and 1,489,046. Unfortunately, preparation of quaternary carboxamide polymers by such methods requires extended reaction times and/or elevated temperatures. As such, substantial amounts of time, capital and energy are required to obtain the desired yields of the quaternary polymers. U.S. Pat. No. 4,049,606 reports higher yields can be obtained by maintaining the pH of the reaction mixture at a first, slightly acidic, pH during the aminomethylation reaction step and at a second, slightly basic, pH during the quaternization reaction step. Unfortunately, the disclosed procedure requires careful control of reaction conditions, e.g., regulation of pH and temperatures to achieve such higher yields.
Alternatively, quaternary carboxamide polymers can also be prepared by reacting the polymer with the previously prepared reaction product of a secondary amine and an aldehyde followed by the quaternization of the polymer using an alkylating agent. See, for example, U.S. Pat. No. 4,010,131. Unfortunately, said method does not substantially reduce the amounts of time, capital and energy required for the preparation of the quaternary polymer. Moreover, said method requires the preliminary formation and isolation of the fairly toxic aldehyde-amine adduct.
In view of the aforementioned deficiencies of the prior art methods for preparing quaternary derivatives of carboxamide polymers, it would be highly desirable to provide a more efficient method for preparing carboxamide polymers.